1. Field of the Invention
This invention relates to an ink-jet recording apparatus and an ink-jet recording method.
2. Description of the Related Art
It is known that in apparatuses of this kind, recording is performed by forming dots on a recording medium. FIG. 10 is a schematic diagram illustrating the configuration of a conventional apparatus of this kind.
In FIG. 10, an ink-jet recording head 1 forms dots on a recording medium by discharging ink. A carriage 2 detachably mounts the ink-jet recording head 1 and performs scanning in a main scanning direction. The scanning of the carriage 2 is realized by the driving force of a CR (carriage) motor 3 which comprises a pulse motor. That is, the driving force of the CR motor 3 is transmitted to the carriage 2 via a driving belt 4, and the scanning of the carriage 2 is guided by two carriage shafts 5 which slidably support the carriage 2.
A conveying roller 6 conveys the recording medium in a sub-scanning direction, and is driven by an LF (line-feed) motor 7.
A control circuit 8 controls the ink-jet recording head 1, the CR motor 3, the LF motor 7 and the like based on a recording signal. A cable 9 transmits a control signal from the control circuit 8 to the ink-jet recording head 1.
FIG. 11 is a block diagram illustrating principally the configuration of the control circuit 8. In FIG. 11, a CPU (central processing unit) 13, comprising a microprocessor, exchanges signals with a host computer 14 via an interface 15, and controls the recording operation of the apparatus shown in FIG. 10 based on recording data stored in a program memory 16, comprising a ROM (read-only memory), or recording data transmitted from the host computer 14 and stored in a buffer memory 17, comprising a RAM (random access memory). That is, the CPU 13 controls the CR motor 3 and the LF motor 7 via motor drivers 22 and 23, respectively, and also controls the discharging driving of the ink-jet recording head 1 via a head driver 21 based on the recording data stored in the RAM 17. An operation panel 18 is provided at a portion of the apparatus shown in FIG. 10. The user can confirm the recording state of the apparatus and input various kinds of commands through the operation panel 18. A sheet sensor 19 detects if the recording medium is present in a recording region by the ink-jet recording head 1.
FIG. 12 is a flowchart illustrating an example of recording control in the above-described conventional apparatus.
When recording data has been transmitted from the host computer 14, the CPU 13 develops the received data into data having the form of ink discharge by the ink-jet recording head 1, and stores the obtained data in a buffer memory for one line in the RAM 17 (step S1201). Then, the ink-jet recording head 1 mounted on the carriage 2 is moved to perform scanning by driving the CR motor 3. Recording is performed by forming dots by discharging ink from the moving ink-jet recording head 1 onto the recording medium (steps S1202 and S1203).
FIG. 13 illustrates a method for forming recording dots at that time.
The ink-jet recording head 1 includes discharging ports, whose number equals H, for discharging ink arranged at a pitch P.sub.D. The diameter of a dot formed by ink discharged from each of the discharging ports is set to an optimum size to cover the pitch P.sub.D. The timing of ink discharge from the ink-jet recording head 1 while performing main scanning is provided so as to be synchronized with driving pulses for driving the CR motor 3. That is, for example, the diameter of a pulley (not shown in FIG. 10) is set so that the moving distance of the ink-jet recording head 1 by a one-pulse drive of the CR motor 3 equals an integer multiple (four times in the case of FIG. 13) of the pitch P.sub.D, and the ink is discharged at a predetermined time interval t.sub.E set by a timer 20 during consecutive motor driving pulses. That is, the time interval t.sub.E is calculated so that the pitch of recorded dots formed from the carriage speed of the CR motor 3 equals P.sub.D. When ink discharge based on the recording data for one line stored in the line buffer has been completed, the recording medium is conveyed, as shown in FIG. 14, by a distance L.sub.n, which equals H.times.P.sub.D, in the sub-scanning direction by the conveying roller 6 by driving the LF motor 7 (step S1205). Then, the carriage 2 is returned to the start position, and the recording operation for one line is completed (step S1206). When the received data still remains, the processing of steps S1201-S1206 is repeated.
Some conventional apparatuses have a low-resolution mode called a draft mode in addition to the above-described recording mode. A recording mode can be selected, for example, through the operation panel 18. In the low-resolution mode, recording is performed while doubling the pitch P.sub.D of dots formed in the above-described ordinary recording mode. FIGS. 15 and 16 illustrate a method for forming dots in the main scanning direction and in the sub-scanning direction in this mode.
In FIGS. 15 and 16, the position of a black dot corresponds to a position where a dot is formed by discharging ink in the draft mode, and the position of a black dot corresponds to a position where a dot is formed in the above-described ordinary printing mode, while a dot is not formed, i.e., recording is not performed, in the low-resolution mode.
As shown in FIG. 15, also in the low-resolution mode, dots can be formed in the main scanning direction with the same time interval t.sub.E as in the ordinary printing mode. Hence, the carriage speed can be increased by reducing the interval t.sub.Md of driving pulses for the CR motor 3 to 1/2 of the interval t.sub.M of driving pulses in the ordinary recording mode. Accordingly, the low-resolution mode is used as a mode to shorten the recording time.
In Japanese Patent Laid-Open Application (Kokai) No. 64-63185 (1989), a technique of supplying colorless ink, which causes a dye to become insoluble, onto a material, on which printing is to be performed, using an ink-jet print head is disclosed.
In Japanese Patent Laid-Open Application (Kokai) No. 55-150396 (1980), a technique of supplying a hydration-resistant agent, which forms a pool with a dye, after performing ink-jet printing of water dye ink is disclosed.
In Japanese Patent Laid-Open Application (Kokai) No. 58-128862 (1983), an ink-jet printing method, in which the position of an image to be printed is previously identified, and printing is performed by superposing printing ink and processing ink, is disclosed. In this method, the image is depicted by the processing ink before depicting the image by the printing ink, or the processing ink is superposed on the previously depicted printing ink, or the printing ink is superposed on the previously depicted processing ink followed by superposing the processing ink thereon.
When forming dots on a recording medium by discharging ink in the draft mode, as is apparent from FIG. 15, the size of each dot recorded in the low-resolution mode generally corresponds to the dot pitch P.sub.D in the ordinary recording mode. Hence, if dots are formed with a pitch of P.sub.D .times.2, a space is present between adjacent dots, and therefore an increase in the density corresponding to the number of formed dots cannot be obtained.
In order to solve such a problem, a method of increasing the size of formed dots can be considered. In this method, however, problems arise in the ordinary recording mode in which, for example, spaces in recorded characters tend to be connected because the amount of discharged ink is too great. Accordingly, in conventional apparatuses, the above-described problem remains unsolved.